The invention is in the field of vacuum tubes, and more particularly relates to a field emission cold cathode acting as an electron emitter in a vacuum tube.
Cathodes are electron emitters used in a wide variety of vacuum tubes, such as cathode ray tubes used in televisions and various microwave tubes used in radar and communications. All of these cathodes must be kept under a high vacuum and heated to a very high temperature ( greater than 900xc2x0 C.) for proper operation.
High vacuum necessitates the use of special manufacturing techniques, such as having a device that is sealed, as well as extensive baking out procedures. Further, these types of cathodes are susceptible to contamination if the cathode is ever removed from vacuum. The high vacuum thus provides a considerable constraint to tube handling, operation, and storage.
The requirement for high temperature operation poses two severe restrictions. The high temperature requires the use of special materials that can withstand the high temperature operation of the cathode. In addition, the heater reduces the energy efficiency and increases system volume, weight, and complexity.
Accordingly, there is a need for a cathode that can operate at low temperatures and have less stringent vacuum requirements, while delivering the same electron emission characteristics as conventional vacuum tube cathodes.
In a preferred embodiment, the invention replaces the heated cathode of a conventional vacuum tube with a field emission cold cathode. The cathode is comprised of a carbon velvet material coated with a low work function cesiated salt and bonded to a cathode surface. Electrons are emitted when a sufficient voltage is applied to the cathode. It is considerably more energy efficient than a conventional vacuum tube and can operate at a lower vacuum level. The carbon velvet material is a material comprised of high aspect ratio carbon fibers embedded perpendicular to a base material. The carbon velvet material anticipated by the present invention can be bonded to any complex-shaped cathode. This cold cathode can replace the heated cathode of any type of vacuum tube, including, klystrons, traveling wave tubes, magnetrons, magnicons, and klystrode/IOT TV transmitters.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing, illustrating by way of example the principles of the invention.